Cold energy storage

ABSTRACT

Disclosed is a cold storage container able to keep its contents cool for long periods without using electricity by using the phenomenon of adsorption. An adsorbent material placed in a conductive material above an insulated vacuum chamber adsorbs water vapor from the melting ice surrounding or above a cold chamber where contents are kept cold. This generates continuous evaporation which cools the water and therefore the contents of the cold chamber.

TECHNICAL FIELD

This invention relates to cold energy storage devices and, more particularly, to adsorption-based cold energy storage devices.

BACKGROUND

Continuous refrigeration is required to store and transport food, fruits, vegetables and health supplies. Bananas, for example, are stored at temperatures between 14 and 18° C.; and vaccines need to be stored in temperatures between 2° C. and 8° C. in order to keep their disease preventing properties. For places where access to electricity is limited, electricity-free cold storage solutions are often required.

A cold chain is a temperature-controlled supply chain that includes a series of refrigerated production and storages. A cold chain maintains a desired low-temperature range right from manufacturing to the end user. The cold chain consists of walk-in chillers, walk-in freezers, refrigerators, refrigerated trucks and cold storage boxes. Cold box storages are typically thermally insulated devices that allow transportation without electricity.

In rural areas, especially in developing countries, electricity is either not available or unreliable with voltage fluctuations. With such conditions, refrigerators cannot operate and products such as vaccines cannot be stored at the required temperatures. Refrigerators and chillers often use mechanical compressors which consume substantial amount of electricity and therefore difficult to operate in such areas. For example, in India, where 70% of the population is rural, only 2% of rural children receive vaccination.

There are different types of cold box storages. A typical cold box uses thermally insulating materials to reduce heat transfer between the content that needs to be kept cold and ambient temperature. This is perhaps the most dominant technology that is used for many applications.

There are other types of cold boxes that enhance the thermal insulation of this commonly used technology by adding a semi/full vacuum chamber around it. Some more advanced cold boxes not only provide thermal insulation, but also proactively generates cooling power for a limited time which significantly improves hold over time.

There are also a number of cold storages or cooling containers that operate based on the adsorption phenomenon. One example is a three-chamber configuration containing vaporized liquid, sorbent and vacuum (Sabin, Thomas, and Steidl, U.S. Pat. No. 5,048,301; 1991). In this system, adsorbent container in located inside the cold box where a valve can control the evaporation. However, in this configuration the dissipation of heat from adsorbent is not efficient. A second example is U.S. Pat. No. 4,759,191; 1988, where an insulated chamber containing the sorbent connected to the liquid chamber (evaporator) via a valve and a liquid-vapor separator. Another configuration is a single-bed adsorption system disclosed by Monma and Mizota having a refrigeration chamber in the middle surrounded by an evaporator containing the liquid and that is surrounded by an adsorbent bed (Monma, Mizota, JP2005299974; 2005). The wall between the refrigeration chamber and evaporator is thermally conductive, while the outer surface of the evaporator between evaporator and adsorbent bed is a thermally insulated layer. Opening a valve between the evaporator and adsorbent chamber starts the operation. However, this configuration can only operate with liquid refrigerants and insulation between the adsorbent bed and evaporator, which is not practically effective. This is due to the fact that even the best insulating materials still conduct heat, yet at lower rate. Therefore, in the by configuration suggested by Monma and Mizota, the heat of adsorption dissipates into the evaporator, which reduces cooling power. Different configurations using the same principle have also been suggested for self cooling drink containers and cans (Claydon, U.S. Pat. No. 6,829,902) (Hidaka, et al., JP2005098647), temperature controlled storage (Eckhoff, et al., U.S. Pat. No. 9,140,476) or a container cooling apparatus (Maier-Laxhuber et al., U.S. Pat. No. 5,440,896).

U.S. Pat. No. 6,688,132 (Smith et al.) discloses another related design for a cooling container in which a mechanism is devised to control the flow of refrigerant and thus control the temperature or duration of cooling. The mechanism involves one or more liquid reservoirs and fluid restriction between the reservoir and evaporator. However, this design is also only usable with liquid refrigerants.

Another related adsorption cooling system is a temperature-controlled portable cooling unit (Eckhoff, et al., U.S. Pat. No. 9,170,053). Its evaporator chamber and desiccant chamber are separated by a vapor conduit where the vapor control unit (valve, controller and sensor) is located.

Innovations and improvements in electricity-free adsorption technology remain highly desirable.

SUMMARY

The following presents a simplified summary of some aspects or embodiments of the invention in order to provide a basic understanding of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some embodiments of the invention in a simplified form as a prelude to the more detailed description that is presented later.

The present invention relates to a self-contained cooling storage, container or device comprising an adsorber unit, an evaporation chamber and an optional area for storage or container. The adsorber unit is located on the top of the system where its outside wall includes a thermally conductive material (e.g. aluminum). Therefore, the produced heat of adsorption can transfer effectively to the ambient air. The evaporator chamber is designed to enable the use of ice as well as other solid or liquid refrigerants. The use of ice provides a wider range of cooling temperature and/or prolonged duration of cooling. There is no valve between the evaporator and adsorbent chamber, which enables to provide a large surface area and therefore maximize the diffusion of vapor into the adsorbent. Furthermore, the thermal insulation between the evaporator and the adsorber unit is provided by vacuum to prevent the adsorption heat affecting the cooling storage.

This invention allows low temperatures to be maintained without continuous supply of electricity by providing a cold storage or carrier whose cooling effect is provided by an adsorption process. The full adsorption refrigeration cycle is not performed in the present cold storage as this system does not have any condenser units. The evaporation process provides the cooling effect and is essential for this operation. A desorption process is also performed during the charging process. The desorption process can be performed either by separating the adsorbent unit or in-situ. In the first case the adsorbent can be heated in the oven or any other heating device. For the second case (in-situ desorption) the adsorbent can be heated via contacting a hot device (e.g. an iron) to the top conductive layer or via turning on a set of heating wires located in the adsorbent.

This invention is a cold storage box which, in addition to the thermal insulation used in standard cold storage boxes, uses the phenomenon of adsorption to provide electricity free cooling power. In laboratory tests, the adsorption extended the hold over time of a standard cold storage box by more than 800%. This allows electricity free storage for several days, weeks or even months below 15° C. which is ideal for many fruits such as bananas. For other applications where lower temperatures are required, the duration of electricity free storage would be shorter depending on temperature requirements. The invention significantly decreases operating costs because of the reduction in electricity consumption, and also allows contents to be shipped over large distances without the need of refrigerated shipment. In addition, it allows for the storage of health supplies such as vaccines to improve accessibility for hard-to-reach populations in rural areas.

The present invention is a sorption-based portable thermal energy storage (TES) device to produce and maintain cooling within a closed space. There are many sorption-based TES devices currently in research and development, although most of them are large and full-scale systems aimed to produce space cooling and heating for buildings and locomotives (see e.g. Li, Hwang, and Radermacker, International Journal of Refrigeration, 2014; 44: 23-35). These systems are stationary devices installed near a heat source, which can be recovered to power the sorption cycles. Closed-loop sorption cycles are common in TES applications where the refrigerants are conserved and undergo thermodynamic cycles in a closed system. The present invention is different in a way that it is a portable cold storage device that is designed to be carried and transported either by manpower, automobiles or equivalent. The present invention only executes a single-stage thermodynamic process instead of a full thermodynamic cycle to produce cooling, thus providing portability by eliminating the condenser, desorber, heat exchanger and piping that are the essential components in large scale full-cycle systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a cross-section of the adsorption cooling storage box in accordance with an embodiment of the invention.

FIG. 1B illustrates another cross-section of the adsorption cooling storage box in accordance with an embodiment of the invention.

FIG. 1C illustrates a cross-section of the adsorption cooling storage box in accordance with another embodiment of the invention.

FIG. 2A illustrates a design of the adsorption cooling storage box.

FIG. 2B shows a photograph of a prototype of the adsorption cooling storage box employed for experiments.

FIG. 3 is a graph of temperature versus time that illustrates the results of a series of experiments comparing a conventional storage box with the adsorption cooling storage box of the present invention for two different adsorbents, namely silica gel and zeolite.

DETAILED DESCRIPTION

The present invention is an adsorption-based cold storage box (or cold energy storage device) which can be used as a transportable carrier or static storage container for carrying or storing contents that are to be kept cool.

Storage Carrier Configuration

In the embodiment depicted by way of example in FIG. 1A, the cold storage box (or simply cold box) includes a cold chamber or container 103 for containing the contents to be kept cooled. The cold chamber or container 103 is made of thermally conductive material and is surrounded by a refrigerant, such as ice. The cold chamber (container) 103 is supported inside the evaporator chamber 102 thus defining a space between the outside of the container 103 and the inside of the evaporator chamber 102. The air in this space is evacuated in operation to create a vacuum between the container 103 and the evaporator chamber 102. The refrigerant is surrounded by insulating walls 106 and an insulating bottom or base. In the cold storage box shown by way of example in FIG. 1A, the insulating walls 106 are disposed on the four sides and also on the bottom (with the bottom acting as a base). The box may have other shapes from what is shown. The adsorber unit 101 is disposed at the top of the cold box and thus acts as the top surface of the cold box. The adsorber unit 101 is thus disposed above both the cold chamber (container) 103 and the evaporator chamber. In some embodiments, the adsorber unit 101 is detachable and thus can be removed from the rest of the cold box. Once adsorbents have been saturated with refrigerant molecules, the adsorber unit 101 can be removed and swapped with a new one that has new adsorbents or a regenerated one whose adsorbents have been regenerated by heating the unit. The adsorber unit 101 includes adsorbent material 111 (e.g. adsorbent powder or granules), a thermally conductive top surface 112, and a mesh 113 that contains the adsorbent and exposes it to the vapor. The adsorber unit 101 can be fastened to the evaporator by clamps, screws, bolts, latches or other mechanical fastening means. The adsorbent material can alternatively be glued or plasma sprayed to the top conductive surface. Furthermore, the side walls of the adsorber unit 101 can be employed to provide heat dissipation. The evaporator chamber 102 (or refrigerant chamber) is equipped with a valve 122, which enables the evaporator chamber 102 to be evacuated after installation of the top part (e.g. after installation of the adsorber unit 101). Using ice as the refrigerant enables a lower pressure (higher vacuum) level to be reached before the refrigerant starts evaporation. Therefore, the chamber maintains a vacuum or partial vacuum (sub pressure condition) throughout the entire transportation process.

In the embodiment shown by way of example in FIG. 1B, the contents from the cold chamber can be removed via a lid, hatch or door 131 in one of the side walls 106, e.g. a front side wall of the storage, without interfering with the vacuum inside. As the ice begins to melt around the container 103 (cold chamber), the water begins to evaporate around 0° C. and, due to the vacuum pressure, it maintains at the saturation vapor pressure of the refrigerants. The molecules of the refrigerant vapor are adsorbed by the adsorbent sitting in the top unit. This allows evaporation to continue. The evaporation releases latent heat of vaporization which cools the water and ice surrounding the cold chamber (i.e. container 103) thereby keeping the cold chamber cool. This process continues until the adsorbent becomes saturated or the refrigerant (e.g. water) is completely evaporated. The latent heat of vaporization of water is significant and therefore the cooling maintains the required temperature for a long period of time without electricity.

When one cycle of cooling has been completed, the adsorber unit 101 is detached and the adsorbent 111 is dried by exposure to a heat source, e.g. an electric heater, fire, sun, etc. The adsorber unit 101 is then reinserted or reattached for the next cooling cycle. The cold storage box is refilled with ice and the space inside the evaporator chamber 102 holding the ice is depressurized using a vacuum pump. After this, the cold storage box can be reused for another cycle of cooling. Alternatively, the adsorber unit 101 can be recharged by heating in-situ. It can be done by heating the conductive surface 112 or by turning on heating wires inside the adsorber unit.

In some embodiments as shown by way of example in FIG. 1C, the cold storage box includes a vapor permeable membrane 126 disposed between the refrigerant in the evaporator and the adsorbent. Also, in some embodiments, sliding sheets 127 can be located between the evaporator and adsorbent to facilitate the control of an exposure area. The sheets can slide on each other to open most of the exposure area (i.e. to increase exposure) or to cover the exposure area (decrease exposure). These sheets can be controlled manually at the start of packaging and vacuuming the chamber. Alternatively, the motion of sheets and therefore exposure area can be controlled automatically, e.g. using an electronic controller and mechanical actuation means.

Storage Box Configuration

The cold storage box has a similar configuration comparing to the carrier box except for that there is no lid 131 at the front of cold chamber (i.e. container 103) to allow excess of contents from outside. The lid shown in FIG. 1B is replaced by thermal insulation walls as illustrated in FIG. 1A or FIG. 1C. The contents are placed inside the cold chamber (container 103), which may be airtight. The container 103 is completely contained inside the evaporator chamber 102 with ice surrounding the container 103 under vacuum. The container 103 (cold chamber) can be accessed by opening the adsorber unit 101. This configuration minimizes the heat penetration into the container 103, and is thus very suitable for a long-term storage application.

It should be understood that, while water is an inexpensive, widely available, and non-harmful refrigerant, there is a possibility to readily use other available refrigerants or add additives to water to change the freezing point or other parameters of the refrigerant.

Additional Features

The following features can be applied to both carrier and storage box configurations.

Temperature Control and Warning

The temperature of the cold box could be controlled, in one embodiment, to maintain the temperature at a certain predetermined level, or within a certain temperature range, by controlling the amount of exposure between the adsorbents and refrigerants. An electrical valve or similar flow control device that connects the adsorber unit 101 and the evaporator chamber 102 could be installed along with temperature and/or pressure sensors inside the evaporator chamber to facilitate the feedback temperature control process. Controlling the exposure area between the adsorber unit 101 and the evaporator chamber 102 effectively controls the rate of adsorption through evaporation. Thus this technique enables the cooling power to be matched with the desired demand.

One or more temperature sensors could alert the user when the temperature has exceeded the desired level. The user is thus able to set the temperature level depending on one or more requirements. Pressure sensors could detect air leakages and warn the user whenever a leak occurs.

Manual Desorption

A fixed or detachable manual vacuum pump could be installed on the evaporator chamber 102 to achieve either the manual desorption process or re-depressurization once the vacuum has been released. Premature vacuum release occurs when adsorbents have not yet reached full capacity and could result from accidentally opening the pressure release valve during the transportation process or by minor system leakages. The system could be re-vacuumed under either situation via the manual vacuum pump. A cold trap can be located between the vacuum pump and valve.

When the adsorbents have reached their full capacity and an additional amount of cooling time is required, the manual vacuum pump could then be operated to reduce the vacuum pressure inside the adsorption unit, thus inducing desorption through the de-pressurization process. Desorbed refrigerant vapor could be released through the vacuum pump and regeneration energy will be supplied from the ambient temperature. A proper ambient temperature is required for a successful manual desorption process.

Use of Multiple Adsorbents

In another embodiment of this invention, multiple adsorbents (such as silica gel and zeolite) may be used at the same time. Since each adsorbent performs better at a specific temperature and vapor pressure, this allows more continuous generation of cooling power at different vapor pressures and temperatures. Therefore, this configuration can help enhancing the efficiency of the cold box and prolonging the hold-over time.

Experimental Results

A series of performance tests have been conducted using the storage box configuration shown in FIG. 2A and FIG. 2B. The temperatures versus time are shown in FIG. 3. These experiments compare the difference in temperature hold-over time for identical cold boxes, employing different adsorbents, namely silica gel and zeolite, versus the cold box without any adsorbent. In the silica gel experiment, 1.4 kg of silica gel desiccants with properties specified in Table 1 were located in one box. In the case of zeolite, 1.27 kg of zeolite granules were employed. In all cases 0.6 kg of ice was initially located inside the refrigerant chamber 102.

FIG. 3 shows the time evolution of temperature of water in the refrigeration chamber in the three cases of cold box without adsorbents, cold box with silica gel adsorbent and cold box with zeolite adsorbent. Under the controlled ambient temperature of 20° C., the cold box with silica gel adsorbent outperforms the one without adsorbents by 7.6 times with a total hold-over duration of 187 hours till 15° C.

TABLE 1 Material Property Value Unit Silica gel Bead Size 0.5-1.5 mm Normal Pore 20-30 Angstrom Opening Bulk Density 850 Kg/m{circumflex over ( )}3 Zeolite Bead Size 2.38-4.76 mm Normal Pore 10 Angstrom Opening Bulk Density >0.64 g/ml

Furthermore, the cold box with zeolite adsorbent outperformed the one without adsorbents by 8.8 times with a total hold-over time of 216 hours. As shown in the graph, the temperature lines of adsorption cases reaches the first plateau at 11° C., and thus the adsorbents in these tests are able to activate at around 11° C. without any control.

The following documents are incorporated herein by reference: (i) Claydon, P. C., “Self-Cooling Can,” U.S. Pat. No. 6,829,902; (ii) Eckhoff, P. H., Peterson, N. R., Tegreene, C. T., Wood, L. L. , “Temperature-controlled Portable Cooling Units,” U.S. Pat. No. 9,170,053; (iii) Eckhoff, P. H., Gates, W., Hyde, R. A., Jung, E. K. Y., Myhrvold, N. P., Peterson, N. R., Tegreene, C. T., Whitemer, C., Wood, L. L., et al., “Temperature-controlled storage systems” U.S. Pat. No. 9,140,476; (iv) Hidaka, H. Kakiuchi, H., Iwade, Y., Takewaki, T., Yamazaki, M., Watanabe, N., “Adsorption Type Cooler,” JP2005098647; (v) Maier-Laxhuber, P., Schwarz, J., Winter, E. R. F., Soltes, J., “Apparatus for cooling a medium within a container,” U.S. Pat. No. 5,440,896; (vi) Monma, T. Mizota, T., “Adsorption Type Refrigerator,”, JP2005299974; (vii) Smith, D. M., Roderick, K. H., Perkes, R. G., Sinclair, V., Warren, L. X., “Cooling Device and Temperature-Controlled Shipping Container Using Same,” U.S. Pat. No. 6,688,132; (viii) Sabin, C. M., Thomas D. A., Steidl, G. V., “Vacuum Insulated Sorbent Driven Refrigeration Device,” U.S. Pat. No. 5,048,301; (ix) Thomas D. A., Sabin, C. M., Cover, J. H., “Miniaturized cooling device and method of use,” U.S. Pat. No. 4,759,191; and (x) Li, G., Hwang, Y., and Radermacker, R., “Experimental Investigation on Energy and Exergy Performance of Adsorption Cold Storage for Space Cooling Application,” International Journal of Refrigeration, 44; 23-35, 2014.

It is to be understood that the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a device” includes reference to one or more of such devices, i.e. that there is at least one device. The terms “comprising”, “having”, “including” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of examples or exemplary language (e.g. “such as”) is intended merely to better illustrate or describe embodiments of the invention and is not intended to limit the scope of the invention unless otherwise claimed.

While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure.

Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the inventive concept(s) disclosed herein. 

1. A cold storage box comprising: a container for containing contents to be kept cool; an evaporator chamber having thermally insulated walls surrounding the container and defining a space between the container and the chamber; and an adsorber unit located above the evaporator chamber, the adsorber unit including adsorbent material, a mesh retaining the adsorbent material while permitting the adsorbent material to be exposed to vapor from the evaporator chamber, and a thermally conductive surface on a top or surrounding sides of the desorber unit.
 2. The cold storage box of claim 1 wherein the container is made of thermally conductive metal.
 3. The cold storage box of claim 1 wherein the space surrounding the container holds ice.
 4. The cold storage box of claim 1 wherein the space surrounding the container holds a refrigerant.
 5. The cold storage box of claim 1 comprising a valve for evacuating air from the chamber.
 6. The cold storage box of claim 1 wherein the space is enclosed within insulating side walls and an insulating base.
 7. The cold storage box of claim 1 wherein the chamber has a hatch on one face for removal and insertion of contents.
 8. The cold storage box of claim 1 wherein the hatch is accessible through one of the side walls.
 9. The cold storage box of claim 1 wherein the adsorber unit is detachable from the box for regenerating the adsorbent material within the absorber unit.
 10. The cold storage box of claim 1 wherein the adsorber unit includes multiple adsorbents having different adsorbent properties.
 11. The cold storage box of claim 1 further comprising a vapor-permeable membrane located between the evaporator chamber and the adsorber unit.
 12. The cold storage box of claim 1 further comprising sliding sheets located between the evaporator chamber and the adsorber unit to control an amount of area of the adsorbent unit that is exposed to the vapor.
 13. A cold storage box comprising: a container for containing contents to be kept cool; an evaporator chamber having thermally insulated walls surrounding the container and defining a space between the container and the chamber; and an adsorber unit located above the evaporator chamber, the adsorber unit including adsorbent material and a thermally conductive surface on a top or surrounding sides of the desorber unit wherein the adsorbent material is plasma sprayed onto the conductive surface. 